High performance generator and motor designs reject waste heat into liquid flowing through the stator slots. Contact of the liquid with the magnetically permeable material of the stator slots and the electrical windings produces a modest convection heat transfer coefficient. On the other hand, the end turns which are the projection of the stator pole windings axially outward from the magnetically permeable stator core containing the slots are difficult to cool as a consequence of the difficulty in directing cooling fluid in intimate contact with the irregular geometry of the windings. As a result, the heat transfer coefficient between the cooling liquid and the end turns is less than that between the cooling liquid and the slots. As a result, the end turns operate at a higher temperature than the slot.
As a consequence of vibration, it is necessary to support the end turns mechanically to prevent their radially inward and outward vibration which can result in failure of the insulation of the windings leading to potential shorts or other electrical problems. Typically, the end turns are mechanically supported with a potting compound and cord. These methods require substantial labor and have a cost impact on the cost of fabricating a motor or generator.
U.S. Pat. Nos. 2,285,960, 2,975,309, 3,075,103, 4,227,108, 4,323,803 and 4,797,588 disclose fluid cooled stators with fluid contacting the end turns. Only U.S. Pat. No. 2,975,309 supports the end turns against deflection radially inward and outward by potting with insulating material. In the '309 patent, fluid is transmitted through a hollow center portion of the conductors and further in passages offset from the slots through the center of the stator. Conduction of the fluid through the center of a hollow conductor provides less surface area for heat transfer than intimate contact with the outside surfaces of the end turns which provides for a more efficient heat transfer.
Containment sleeves have been used in the prior art to prevent cooling fluid from flowing into the air gap between the stator and the rotor. Cooling liquid, such as oil in the air gap, creates windage losses which reduces the overall efficiency of operation of an electric machine. Self-excited electric power generators of the type utilized in airframes use a permanent magnet generator to generate the electric field in the stator of an exciter with the exciter rotor producing three phase alternating current which is rectified by a rotating three phase rectifier assembly rotating with the exciter rotor to produce DC used for creating the electric field in the main generator. For electric machines having high output it is necessary for the exciter rotor to produce high current outputs for generating the necessary current which is rectified by the rectifier assembly to create the electric field for the main generator. In the prior art, one cooling technique is to spray the windings of the rotor with oil to reduce the heat flux produced by the rotor windings. This technique has the disadvantage of creating windage losses in the air gap between the exciter, stator and rotor.
The three phase fullwave rectifier of a self-excited electric power generator is typically mounted inside the annulus of the exciter rotor. Cooling fluid, such as cooling oil, is circulated through the interior of the rotor assembly.
Sleeves mounted between the stator and rotor of an electric machine are known. U.S. Pat. No. 2,698,911 discloses a stator sleeve which is inserted within the sleeve in the air gap between the stator and the rotor. The stator sleeve is made from stainless steel. The purpose of the sleeve is to prevent water from entering the stator. The sleeve is designed to be rigid to prevent bulging due to heat generated in the motor or to pressure of the oil or plastic material utilized to fill interstices in the windings. U.S. Pat. No. 2,967,960 discloses a submersible motor having a stainless steel liner disposed within the annulus of the stator in a manner similar to that disclosed in U.S. Pat. No. 2,698,911 discussed above. U.S. Pat. No. 3,727,085 discloses a stator sleeve which is formed from a high temperature non-conductive and non-magnetic material which may be a wound fiberglass material which is impregnated by a high temperature epoxy resin as a binding agent. U.S. Pat. No. 4,492,889 discloses a submersible motor having a sleeve which lines the interior of the annulus of the stator which is fabricated from carbon fiber reinforced plastic. Furthermore, the '889 patent discloses that the stator sleeve may be manufactured from plastic reinforced with glass or metal fibers. The stator sleeve of the '889 patent is not disclosed as having a multiple laminar structure nor is orientation of reinforcing fibers disclosed. U.S. Pat. No. 4,729,160 discloses a composite sleeve for an electric motor which is bonded to the rotor of a motor.